[volt-nuts] Finally got around to modifying my Fluke 845ab with LED's

[Chuck Harris]

Hi Mark,

I have an itty bitty white led, probably called a T-1 size, and it
glows dimly for a long time after you shut it down.  They all pretty
well have to.

I think what you are seeing with your analyzer is the blue/UV component
that drives the phosphor element.  It will run just as fast as any old
style LED.

I also think that the blue/UV component, which is very bright, is what
is driving Dallas's chopper.

But enough on that.  I wasn't trying to criticize, just make mention of
something I noticed in my own work.
Where I got to thinking of this is when I burned out the strobe tube
in my G-R strobotach.  Replacement tubes were in the $300 range, so I
knew that would never happen, so I was thinking of making a solid state
replacement using a handful of those wonderful little white LED's.
They would certainly be bright enough, but I'm pretty sure the phosphor
hang would make them unsuitable for stopping motion... your eye would
see a blur instead of the razor sharp image you get with the strobe tube.

-Chuck Harris



Mark Sims wrote:
> I would probably use green or yellow LEDs,  but the white ones should not be a
> problem. I built an LED analyzer/integrating sphere and one of the features is a
> circuit that optically measures the LED driver PWM frequency.  It can also detect
> the minute variance in LED intensity from an LED driven by a 950 kHz boost
> converter.  It also had no problems with a white LED driven at 4 MHz from a signal
> generator.  You see the long persistence phosphors mainly in large lighting LEDs
> and not in small indicator LEDs. _______________________________________________
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